1. Field of the Invention;
The present invention relates to surveying methods and devices. In particular, the present invention relates to surveying hubs for locating a traverse point and a method for use thereof.
2. Discussion of Background:
The art of surveying is thousands of years old, as old as ownership and taxation of real property which began as early as 1400 BC in Egypt. Early Egyptian surveyors used ropes for distance measurements and plumb bobs, leveling frames, and channels filled with water to determine if a foundation were level. Roman surveyors developed the use of the odometer and a device called a groma, comprising two horizontal crossarms fastened at right angles with plumb bobs attached to the ends of the crossarms, for laying off right angles. The surveyor's chain was developed in the early 1600 and is in use today. Although there have been great improvements in materials used for chains and tapes. Steel is still the most common material for a chain but fiberglass and special alloys such as INVAR and woven tapes provide better performance and less structural variation as a result of thermal expansion and elastic stretching.
Recently the number of improvements in the equipment used for measuring distance has increased dramatically. Distance is now frequently measured with electronic distance measurement (EDM) instruments that rely on the time for a beam of sound or light rays (including visible, infrared, laser, radar and microwave) to travel to a reflector and back. The beam of sound or light rays emitted by the EDM instrument positioned at a fIrst location are reflected back by a prism, usually mounted on a pole, positioned at a second location to determine the distance between the two locations. The accuracy and ease of use of these instruments have been improved and their size and cost reduced to the point where they are essential in modern land surveying.
Technological advances have also been made in optical equipment and leveling devices used inland surveying. Minicomputers are built into many of these devices to perform the calculations related to land surveying in an attempt to improve calculational accuracy in the field.
Typically land surveying is performed as follows. When measuring distances greater than 35 feet, an instrument operator sets up an EDM instrument on a tripod over a known point at a first location, sometimes called a traverse station or traverse point. A second member of a survey crew, the "rod man", handles the prism pole. The rod man will pace off a distance along a line from the first traverse point to a second location to locate approximately the position of the second traverse point. The EDM instrument operator also instructs the rod man to move the prism to the left or right in order to establish the correct, pre-determined traverse line. No numerical increments are communicated in this left/right movement.
An experienced rod man can pace off a distance of 200 feet and usually be within 5 to 1O feet of the true distance. The rod man, then, turns his prism to face the EDM instrument operator who in turn places him on line and electronically measures, or "shoots", that distance. The EDM operator then communicates orally or by radio to the rod man to move the prism forward or backward some specific distance to achieve the exact total distance required to establish the second traverse point. The rod man estimates this communicated distance and repositions the prism pole, so the EDM instrument operator can take another "shot." This process is repeated until the prism is within approximately 0.05 feet of the desired second traverse point. On this point a hub, which is a wooden stake approximately 11/2 inches by 11/2 by 12 inches or less, is driven into the ground so that its upper surface is flush with the surface of the ground. A plumb bob is held over the stake by the rod man and sighted on by the instrument operator. When the plumb bob is aligned with the traverse line, a temporary mark is made in the hub's top surface. Next, the prism rod is placed on the temporary mark, and the EDM process continues until the exact distance (measured in hundredths of a foot) is located. A tack is placed in the surface of the hub to mark this location permanently.
For the rod man to arrive at this exact point, the EDM instrument operator may have to take a number of measurement readings, often four or more. The number of readings, or "shots", that are necessary depends on how adept the rod man is at judging distances. A rod man is usually paid a low wage, and turnover in employment is high. Consequently, instrument operators are constantly faced with new, unskilled rod men. Location of an exact point can therefore be time-consuming and frustrating for both crew members.
There are a number of hubs designed to carry or contain information about the survey. See for example U.S. Pat. Nos. 4,127,972 issued to Reimoser, 546,025 issued to Northam, and 191,919 issued to Bonner. However, there is none that helps to locate a point.
Only recently has EDM technology made the measuring of distances in land surveying possible without a chain; therefore, not until recently has there been a need for an improved hub, designed to compliment and assist EDM instrument use in land surveying.
There is a need for accuracy and speed in every aspect of land surveying. When tapes and chains were the principle means of measuring distances, the chain could be placed over the hub while being stretched between traverse points, so the point where the second traverse point lay was automatically located. Now, as surveyors have moved to the use of EDM instruments, the method of locating the second point has taken on a somewhat intangible characteristic. However, the design of the hub has not evolved with the rest of land surveying technology.